The present invention relates to an improved method of constructing a ball valve element and, more particularly, to a ball valve assembly which will operate reliably over a broad temperature range.
In a number of applications, ball valve elements are frequently subjected to elevated temperatures which can cause the metal valve element to expand and become jammed against its associated valve seats. This is particularly troublesome where scale deposits have built up on the ball itself or the valve seats. Attempts to turn a jammed ball element can result in stem and/or seal failure.
In addition, a phenomena has been recognized where the ball inside the valve assembly may become very much hotter than the air outside the assembly as well as much hotter than the valve housing itself as the ball valve element is not able to radiate heat as efficiently as the valve housing. As a consequence, the ball valve element will experience greater thermal expansion than does the valve housing. In some cases, particularly where the valve seats are made of metal, binding of the ball valve element may occur. To obviate this difficulty, the prior art has proposed the use of movably mounted metal seats. However, this solution suffers from the disadvantage that it is relatively expensive to manufacture and is subject to failure such as when a hard particle comes between the metal seat and the ball valve element.
Accordingly, it is an object of the present invention to provide an improved ball valve assembly where thermal expansion of the ball valve element can be accommodated without requiring a replacement of the conventional fixed valve seat.
In a preferred embodiment, the method of the present invention comprises the step of removing a portion of the material of the ball valve element along a line parallel to the through bore of the ball. With a portion of the material of the ball removed, the ball will be able to become compressed when subjected to an external force much more readily than has heretofore been possible. Further, the much greater degree of compressibility of the ball will greatly minimize binding of the ball in its associated valve housing. Moreover, by facilitating the compression of the ball, thermal expansion of the ball is significantly less likely to result in jamming of the ball between metal or other hard seats.
The foregoing and other advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: